(i) Field of the Invention:
This invention relates to novel medical compositions for external applications.
(ii) Description of the Prior Art:
As is well known in the art, medicines have been ordinarily dosed by several ways, i.e. perorally, rectally or hypodermically, of which peroral administration is widely used. However, the peroral dosage involves the disadvantage that it may bring about adverse side effects such as gastroenteric trouble, inappetence, vomit, stomachache and the like, and that the efficacy is shown, in most cases, only on a large dosage of a medicine. For the purpose of overcoming the above disadvantage, external medicines being applied percutaneously have recently been developed as expected to more safely develop the pharmaceutical efficacy while lowering the side effects, and are, in fact, commercially sold. However, the percutaneous absorption of medical ingredients in the known external medicine is not always satisfactory and the above purpose has not been achieved well. This is because the horny layer of the skin, which constitutes the outermost layer, has the physiological function as a barrier against substances to be passed into the body, so that even if a base which is employed in ordinary external medicines is used along with medically effective ingredients, the ingredients are not percutaneously absorbed satisfactorily in most cases. Accordingly, it is necessary to cause the medical substances to be passed through the horny layer in order to enhance the percutaneous absorption of the medical substances.
To this end, it is general to add so-called percutaneous absorption enhancers to the base. For instance, there are known, as such enhancers, amide compounds such as dimethylsulfoxide, dimethylacetamide, dimethylformamide and N,N-diethyl-m-toluamide, azacycloalkane-2-one derivatives such as 1-dodecylazacycloheptan-2-one, esters of alcohols and carboxylic acids such as isopropyl myristate, isopropyl palmitate, diethyl sebacate, diisopropyl adipate and the like, and crotonyl-N-ethyl-o-toluidine.
However, these absorption enhancers have not the satisfactory absorption effect. If these enhancers are added to external medicines, the practical pharmaceutical effect may not be obtained. Alternatively, the absorption enhancers may irritate the skin and may attack synthetic resins because of the ability as strong solvent, so that irritative substances or sensitizing substances are eluted from the container for medicine or clothes. This will limit the application or use of the enhancer, thus presenting problems in practical application.